Apparatus for managing the energy supplied to a low-voltage system of a motor vehicle that comprises an energy-recovery stage, and corresponding method

ABSTRACT

An apparatus and a method for managing the energy supplied to a low-voltage system of a motor vehicle that comprises an energy-recovery stage. The low-voltage system, operating at a first voltage, comprises a battery, a system for charging the battery, and motor-vehicle loads supplied by the battery and/or by the alternator. A high-voltage system operates at a second voltage higher than the first voltage. The high-voltage system includes the vehicle energy-recovery stage, which supplies the second voltage. The second voltage is supplied through an intermediate energy-storage system and a DC-DC converter, which converts the second voltage into the first voltage on the low-voltage bus. A module regulates the alternator, that activates at least one first operating mode in which the alternator regulates a voltage of the battery at a nominal operating value.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to and all the benefits ofItalian Patent Application No. 102016000112523, filed on Nov. 8, 2016,which is hereby expressly incorporated herein by reference in itsentirety.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to an apparatus and a method for managingthe energy supplied to a low-voltage system of a motor vehicle thatcomprises an energy-recovery stage. The low-voltage system, operating ata first voltage, comprising a battery, which supplies said first voltageon a low-voltage bus, a system for charging the battery, which includesan alternator for supplying a charging voltage to said battery, andmotor-vehicle loads supplied by the battery and/or by the alternator, ahigh-voltage system, which operates at a second voltage higher than thefirst voltage. The high-voltage system includes the vehicleenergy-recovery stage, which supplies the second voltage. The secondvoltage is supplied through an intermediate energy-storage system and aDC-DC converter, which converts said second voltage into the firstvoltage on said low-voltage bus, comprising a module for regulating thealternator, that activates at least one first operating mode in whichthe alternator regulates a voltage of the battery at a nominal operatingvalue.

2. Description of the Related Art

In the automotive sector, energy-recovery systems are known. Inparticular, known to the art are energy-recovery systems that useregenerative shock absorbers, which convert movements of the shockabsorber into electrical energy.

In this context, for example, of particular interest from the standpointof conversion efficiency are regenerative shock absorbers, which convertthe linear motion of the stem into a rotary motion of the shaft of anelectric generator, from which it is hence possible to recover, in theform of electricity, the energy that would otherwise be dissipated inthe form of heat. It is known to perform this conversion via mechanicalor hydraulic means so that rotation of the shaft of the electricgenerator is always in the one and the same direction, irrespective ofthe direction of movement of the stem. This enables a better efficiencyof conversion of the energy, from kinetic into electrical. The electricgenerator is usually a DC generator, which supplies a DC voltage atoutput. If, instead, a synchronous generator is employed, an inverter isused. Either way, it is in any case necessary to use a DC-DC converterto adapt the output voltage of the electric generator to the battery ofthe vehicle.

It is likewise known to use a converter stage for conversion from highvoltage to low voltage, specifically a DC-DC converter the outputvoltage of which is controlled in order to match it to the batteryvoltage, as in the case of the regulator of an alternator.

Illustrated in FIG. 1 is a circuit diagram representing anelectro-mechanical model of a known energy-recovery apparatus,designated as a whole by the reference number 10. Designated by 11 is ashaft of an electric generator 12, associated to which are an angularvelocity {dot over (θ)} and a torque τ. R_(og) denotes the outputresistance of the electric generator 12, for example, a DC generator,whilst denoted by R_(e) is the equivalent resistance of the circuits ofthe portion of apparatus downstream of the electric generator 12, i.e.,the resistance seen by the electric generator 12, the equivalentresistance R_(e) being regulated, for example, by the aforementionedinverter. Denoted by V_(og) is the loadless voltage of the electricgenerator 12, denoted by I_(g) is the current of the generator 12, anddenoted by V_(inDCDC) is the voltage that is set up on the equivalentresistance R_(e).

Consequently, from the foregoing discussion, it follows that it ispossible to control damping of the shock absorber by acting on theequivalent resistance R_(e) seen by the electric generator 12; however,the fact of having to act on the equivalent resistance R_(e) to controldamping rules out the possibility of operating, as in otherenergy-harvesting systems, by matching the impedance of the DC-DCconverter to the output impedance of the electric generator 12 in orderto maximise power transfer.

Illustrated in FIG. 2 is an apparatus, designated as a whole by thereference number 90, for managing the charge of a battery 14.

The aforesaid apparatus for managing battery charge comprises anenergy-recovery stage 30, which includes a plurality of regenerativeshock absorbers 12, in particular four regenerative shock absorbers,associated to respective AC-DC converters in the form of inverters 13,the outputs of which are gathered in a single output node of theenergy-recovery stage 30.

The output node of the energy-recovery stage 30 basically corresponds toa high-voltage bus HV, formed on which are a voltage V_(inDCDC), whichis the voltage on the DC side of the inverters 13, and an inverteroutput current I_(outINV), which is the sum of the four currents atoutput from the inverters 13. The voltage V_(inDCDC) of the high-voltagebus HV is sent to the input of a high-voltage/low-voltage converterstage 50, which, in the example, comprises a DC-DC converter 23, set onwhich, in parallel with the input, is a storage element, i.e., acapacitance, C_(DC). In variant embodiments, the storage element may bea battery. At input to the DC-DC converter 23 is an input currentI_(inDCDC) that is equal to the inverter output current I_(outINV) minusthe current that flows in the storage element C_(DC). Of course, in thepresent context, the voltage on the high-voltage bus HV is defined ashigh with respect to the voltage on the other side of the DC-DCconverter 23, i.e., on the low-voltage bus, which is instead at a lowervoltage, and in general corresponds to the voltage of the electricalsystems of the vehicle, usually 12 V.

In systems like the one described, where a higher-voltage system isconnected, by a converter, to a lower-voltage system, namely, to theelectrical systems connected to the battery of the vehicle, inparticular of the motor vehicle, the high-voltage bus HV is referred tohereinafter as “DC-link bus”, and the storage element C_(DC) is referredto hereinafter as “DC-link capacitance” in so far as the DC-linkcapacitance in general corresponds to the capacitor connected at theinput of the DC-DC converter 23, where the DC voltage to be converted toa lower voltage arrives. The DC-link capacitance is usually obtained viaan electrolytic capacitor or a film capacitor that uncouples the inputof the DC-DC converter.

The above DC-link capacitance C_(DC) in the example described providesan intermediate energy-storage stage 40 at the input of the DC-DCconverter 23. The voltage of the DC-link bus has, for example, a valueof 48 V.

A DC-DC converter 23 is driven so as to control simultaneously the inputvoltage on the above storage capacitor C_(DC) and an output currentI_(outDCDC) towards the low-voltage bus LV, i.e., the circuitsdownstream of the output of the DC-DC converter 23. The DC-DC converter23 is generally a simple current-limited voltage regulator. Setting ofthe output current of the DC-DC converter 23 is made on the basis of theinformation on the battery-voltage set-point coming from the controlunit in which the energy-management strategies reside and is generallyavailable on the LIN (Local Interconnect Network) of the vehicle. Thebattery 14 is also connected to an alternator 60, which applies theretoa charging voltage V_(ALT). A vehicle control unit 70, in particular theengine control unit, applies energy-management strategies viacorresponding energy-management signals EM sent to the alternator 60.These energy-management strategies reside in the aforesaid control unit70, and in particular regulate the charging voltage V_(ALT) supplied bythe alternator 60. Alternators of this type with charging voltage thatcan be controlled externally are usually defined as “smart alternators”.

The apparatus illustrated in FIG. 2 presents some drawbacks.

In the first place, it is difficult to control the vehicle low-voltagebus in the presence of a number of generator devices, such as are thealternator and the regenerative shock absorbers, remaining in line withthe existing energy-management strategies, i.e., with the voltage set bythe smart alternator under the control of energy-management controlsignals sent by the engine control unit. Likewise, it is difficult tomanage the DC-DC converter so as to regulate simultaneously the outputcurrent (and voltage) and the input voltage. It is also problematical tocontrol the apparatus when the battery-voltage set-point is notavailable to the control modules, for example, the control units, as inthe case where the alternator is of a classic type, without anypossibility of external control, or else during acceleration, where thevoltage set-point, even if it exists, cannot be used as such.

SUMMARY OF THE INVENTION

The object of the present invention is to provide an improved apparatusand an improved method that will enable the drawbacks referred to aboveto be overcome.

According to the present invention, the above object is achieved thanksto an apparatus and to a corresponding method having the characteristicsrecalled specifically in the ensuing claims.

To this end, the present invention relates to an apparatus and a methodfor managing the energy supplied to a low-voltage system of a motorvehicle that comprises an energy-recovery stage. The low-voltage system,operating at a first voltage, comprises a battery, which supplies thefirst voltage on a low-voltage bus, a system for charging the battery,which includes an alternator for supplying a charging voltage to saidbattery, and motor-vehicle loads supplied by the battery and/or by thealternator, and a high-voltage system, which operates at a secondvoltage higher than the first voltage. The high-voltage system includesthe vehicle energy-recovery stage, which supplies the second voltage.The second voltage is supplied through an intermediate energy-storagesystem and a DC-DC converter, which converts the second voltage into thefirst voltage on the low-voltage bus, comprising a module for regulatingthe alternator, that activates at least one first operating mode inwhich the alternator regulates a voltage of the battery at a nominaloperating value.

Other objects, features and advantages of the present invention will bereadily appreciated as the same becomes better understood after readingthe subsequent description taken in connection with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described with reference to the annexeddrawings, which are provided purely by way of non-limiting example andin which:

FIG. 1 is a circuit diagram representing an electro-mechanical model ofa known energy-recovery apparatus;

FIG. 2 is an apparatus for managing the charge of a battery;

FIG. 3A represents a flowchart illustrating an embodiment of themanagement method described herein;

FIG. 3B represents a flowchart illustrating an embodiment of themanagement method described herein;

FIG. 4 shows a plot representing currents and powers used by themanagement method described herein;

FIG. 5 is a schematic illustration of an example of DC-DC converter usedby the apparatus described herein;

FIG. 6 illustrates plots of currents in the converter of FIG. 5;

FIG. 7 is a block diagram of an embodiment of the control loopimplemented by the apparatus described;

FIG. 8A details the energy-storage system and the signals that areformed therein;

FIG. 8B further details the energy-storage system and the signals thatare formed therein;

FIG. 8C still further details the energy-storage system and the signalsthat are formed therein;

FIG. 9 illustrates a circuit diagram of the high-voltage portion of avariant embodiment of the apparatus described herein;

FIG. 10 illustrates control signals and signals that are formed in theapparatus of FIG. 9;

FIG. 11 is a schematic illustration of an additional load circuit usedin the solution of FIG. 9;

FIG. 12 illustrates a circuit detail of an additional load circuit usedin the solution of FIG. 9; and

FIG. 13 illustrates a circuit detail of a variant embodiment of theadditional load circuit used in the solution of FIG. 9.

DETAILED DESCRIPTION OF THE INVENTION

In brief, the solution according to the invention regards an apparatusfor managing the energy supplied to a low-voltage system of a motorvehicle that comprises an energy-recovery stage,

-   -   the low-voltage system, which operates at a first voltage,        including:        -   a battery, which supplies the first voltage on a low-voltage            bus,        -   a system for charging the battery, which comprises an            alternator for supplying a charging voltage to the battery,            and        -   motor-vehicle loads supplied by the battery and/or by the            alternator,    -   the vehicle comprising a high-voltage system, operating at a        second voltage higher than the first voltage, the system        comprising the vehicle energy-recovery stage, which supplies the        second voltage,    -   the second voltage being supplied through an intermediate        energy-storage system to a DC-DC converter, which converts the        second voltage into the first voltage on the low-voltage bus,    -   the apparatus including a module for regulating the alternator,        and that activate at least one first operating mode, in which        the alternator regulates a voltage of the battery at a nominal        operating value;    -   comprising detecting information on the regulated voltage in        order to detect the operating mode;    -   upon detection of the first operating mode, the apparatus        carries out a procedure of regulation of the DC-DC converter        comprising:        -   an operation in which a current required by the vehicle            loads is estimated;        -   an operation in which the value determined by the ratio            between the power supplied by the energy-recovery stage and            the battery voltage is calculated;        -   an operation in which a pre-set fixed value that enables            sizing of the DC-DC converter at a given value of desired            average transferrable power is considered;        -   an operation of evaluating the lowest of the three values,            namely, the estimated required current, the ratio, and the            pre-set fixed value; and        -   an operation of limitation by the DC-DC converter of the            output current to the lowest of the above three values,            namely, the estimated required current, the ratio, and the            pre-set fixed value.

According to the solution described herein, the alternator 60 is, in apreferred embodiment, of a smart-alternator type; i.e., it is analternator that can vary its own charging voltage V_(ALT). The chargingvoltage V_(ALT) is supplied on the communication networks of the motorvehicle via the control signals sent by the control unit 70 of thevehicle, in particular the energy-management signals. The solutiondescribed herein may apply, however, also to variant embodiments inwhich a conventional alternator is used. As is known, the conventionalalternator must remain at an internal reference voltage of its own. Atarget battery-voltage value is not hence available on the communicationnetworks of the motor vehicle, but it is envisaged, for example, toestimate this target value on the basis of recent observations made whenthere is no transfer of energy from the DC-DC converter. In other words,the apparatus is configured for detecting information on the regulatedvoltage from an estimation of the value of a charging voltage V_(ALT) ofthe battery 14 obtained by detecting the value thereof in one or moreworking steps of the apparatus 90, in which there is no transfer ofenergy from the DC-DC converter 23.

The above alternator 60, which in the example described is a smartalternator, under the control of the control unit 70, has threeoperating modes, which are usually linked to different operatingconditions of the motor vehicle.

A first, normal, operating mode envisages that the alternator 60regulates the voltage of the battery 14 at a nominal operating value,making this regulation at a nominal value that depends, for example,upon the temperature and that responds to variations of the load. Thisfirst, normal, operating mode is usually associated to given conditionsof state of charge (SOC) of the battery, defined specifically within arange from 70% to 80%. The first, normal, operating mode is implementedby driving the alternator 60 via the energy-management signals EM, inparticular by supplying, as indication of nominal operating valuenecessary to obtain a nominal battery reference voltage of 12 V, forexample, a charging voltage value V_(ALT) of 13.8 V that the alternator60 seeks to maintain as a function of the variation of other parameters,such as the loads. This is in general the prevalent operating mode,associated to a condition where the vehicle is travelling at asubstantially constant speed, where the variations are mostly linked tovariations of the loads.

A second operating mode, here referred to as “braking operating mode”because it is normally used when the motor vehicle is braking, envisagesthat the alternator 60, for example, in braking and coasting conditions,regulates the voltage of the battery at a battery-voltage valueincreased with respect to the low voltage of the low-voltage bus, forexample, 15 V.

A third operating mode, here referred to as “acceleration operatingmode” because it is normally used when the motor vehicle isaccelerating, envisages that the alternator 60, in conditions ofacceleration with charging disabled, regulates the battery voltage at avalue slightly lower than the voltage of the low-voltage bus, inparticular, for example, 11.8 V for a low voltage of 12 V.

Energy-management strategies, which are stored in and are under thecontrol of a control unit, i.e., a device that includes at least oneprocessor, of the motor vehicle (normally, the engine control unit),link the driving conditions, in particular the aforementioned threeconditions of normal driving, braking, and acceleration, to the threeoperating modes. These strategies are in general in themselves known tothe person skilled in the sector, and will not be described in detail.

The output of the above energy-management strategy is a battery-voltagereference V_(bat) _(_) _(ref) made available (normally on thenetwork—LIN—of interconnection between components of the vehicle) by thecontrol unit 70 and used by the smart alternator 60.

As has been mentioned, the strategy implemented by the energy-managementprocedures EM normally resides in the engine control unit (ECU) butcould reside elsewhere, for example, in the body computer of the motorvehicle. The module controlled through the energy-management proceduresEM in the control unit 70 is usually only the smart alternator 60, whichreceives the battery-voltage reference V_(bat) _(_) _(ref).

The solution described herein envisages, instead, supplying the abovebattery-voltage reference V_(bat) _(_) _(ref) also to the DC-DCconverter 23, which uses it to implement a control method, preferably ina logic control module of its own, for selecting a procedure forregulation of the output voltage and current of the DC-DC converter fromamong the regulation procedures 200, 300, and 400 available to the DC-DCconverter.

In this regard, FIG. 3A illustrates a flowchart representing theenergy-management method 100 described herein, where, in a step 110there is carried out acquisition of the battery-voltage referenceV_(bat) _(_) _(ref) that is defined on the basis of theenergy-management strategy EM described above, which defines the first,second, or third operating mode of the smart alternator 60, stored in acontrol unit 70, normally the engine control unit.

Hence, as illustrated in the figure, in a step 120 a check is made onthe value of the battery-voltage reference V_(bat) _(_) _(ref).

If the value corresponds to the nominal low-voltage value, for example,it is higher than 11.8 V and lower than 15 V, a first regulationprocedure 200 is carried out.

If the value is slightly lower than the voltage of the low-voltage bus,for example, 11.8 V for a low voltage of 12 V, a second regulationprocedure 300 is carried out.

Hence, in general, the voltage that starts off the regulation procedure200 is lower than the voltage that starts off the regulation procedure300 and higher than the one that starts off the regulation procedure400.

If the above value is a battery-voltage value increased with respect tothe low voltage of the low-voltage bus, for example, 15 V, a thirdregulation procedure 400 is carried out.

The first regulation procedure 200 and the other procedures 300, 400determine integration of the energy-recovery (or energy-harvesting)module 30, also acting on the DC-DC converter 23, i.e., on the stage 50,as a function of values, in particular the battery-voltage referenceV_(bat) _(_) _(ref), supplied by the energy-management strategies EMalready existing for control of the low-voltage side, more specificallythe alternator 60. These strategies may, of course, be more complex, ata vehicle level.

The DC-DC converter 23 must acquire, for example via the localinterconnection network (LIN), in addition to the battery-voltagereference V_(bat) _(_) _(ref) acquired in step 110 by the control unitwhere the energy-management system EM resides, in the example the enginecontrol unit 70, other values that are used for carrying out theregulation procedures 200, 300, 400. In particular, the currentset-points are acquired from the inverters 13, plus other informationpresent on the CAN bus, for example which are the loads activated. TheDC-DC converter 23 must moreover measure the input and output voltagesto make the necessary regulations.

As has been mentioned, preferably the DC-DC converter 23 isself-regulated; i.e., it contains a logic control module, for example, amicroprocessor, which, on the basis of the inputs listed above,implements the method 100, in particular the steps 110 and 120 and theprocedures 200, 300, or 400. As an alternative to the logic controlmodule inside the DC-DC converter 23, there may be an external controlmodule, which executes the procedures 200, 300, 400 once again as afunction of the information on the inputs listed above.

The first regulation procedure 200 carries out regulation in the contextof an energy-management strategy EM, such as that of the first, normal,operating mode, which takes into account, for example, the temperature,in particular in SOC conditions of 70% to 80%, and indicates a voltagereference equal to the nominal low-voltage value. A SOC condition of 70%to 80% is the optimal one for regenerative recovery, in particularduring braking.

Hence, the first regulation procedure 200 gets the energy-recoverymodule 30 to supply a power, on the low-voltage bus, without raising thelevel of voltage V_(bat) of the battery 14 set by the smart alternator60, in particular without raising it with respect to the nominalcharging voltage value V_(ALT), for example, 13.8 V.

This would be possible by setting the DC-DC converter at a voltageset-point value, i.e., a voltage V_(outDCDC) at output from the DC-DCconverter 23 that is a little higher than the battery voltage valueV_(bat) given by the energy-management signals EM coming from thecontrol unit 70. However, this would mean not charging the battery 14 inaccordance with the vehicle strategies; in particular the battery 14would be charged with higher voltage and current.

In this context, the first regulation procedure 200, representedschematically in the flowchart of FIG. 3B, comprises, instead:

-   -   an operation 210, in which a current I_(LS) required by the        vehicle loads is estimated;    -   an operation 220, in which the value determined by the ratio        between the power supplied by the inverter 13, P_(outINV), and        the battery voltage V_(bat) is calculated; and    -   an operation 230, in which a pre-set fixed value I_(F) that        enables sizing of the DC-DC converter 23 at a given value of        average transferrable power, i.e., the maximum value for which        the converter is sized, is considered.

The steps 210, 220, 230 are carried in parallel, and their results,namely, the current values I_(LS), P_(outINV)/V_(bat), and I_(F), aresupplied in a step 240, which then envisages evaluation of the lowest ofthe three values I_(LS), P_(outINV)/V_(bat), and I_(F). Then, in a step250 an operation is selected of limitation by the DC-DC converter 23 ofthe output current I_(outDCDC) to the lowest of the three current valuesI_(LS), P_(outINV)/V_(bat), and I_(F); i.e., the output current islimited to the lowest of the three values.

In particular, in step 250:

-   -   if the current I_(LS) required by the vehicle loads is the        current of lowest value, the DC-DC converter 23 limits the        output current I_(outDCDC) to a value corresponding to said        estimated required current I_(LS); in this way, the DC-DC        converter 23 supplies only part of the current necessary to the        vehicle loads, whilst the battery 14 continues to be supplied by        the smart alternator 60 at the voltage fixed by the vehicle        energy-management strategy EM; this limitation guarantees the        correct battery voltage V_(bat) in so far as, in all situations,        the charging current is managed by the alternator 60;    -   if the current given by the ratio P_(oitINV)/V_(bat) is the        current of lowest value, the output current I_(outDCDC) of the        DC-DC converter 23 is limited to the value of this ratio        P_(oitINV)/V_(bat); in fact, in particular at low levels of        input power, P_(inDCDC), limitation to the estimated current        I_(LS) of step 210 may be excessive, causing an excessively        rapid discharge of the storage element, i.e., the capacitor        C_(DC), and consequently a high ON-OFF switching frequency of        the DC-DC converter 23; this jeopardizes the shape factor: the        power is transferred in a markedly pulsed way; the behaviour in        these situations is improved by introducing a limitation of the        output current I_(outDCDC) to the value P_(outINV)/V_(bat),        which imposes the minimum useful output current for complete        transfer of the input power P_(inDCDC); this improves the shape        factor; the input power P_(inDCDC) may be obtained by reading        the voltage V_(inDCDC) on the high-voltage bus HV and from the        sum of the currents I_(inDCDC) set for the four inverters 13;    -   if the current given by the pre-set fixed value I_(F) is the        current of lowest value, the output current I_(outDCDC) of the        DC-DC converter 23 is limited to this value.

For each load current value there exists a critical input powerP_(inDCDC) that determines, in step 250, switching from one type oflimitation to another.

Illustrated in FIG. 4 is the plot of the output current I_(outDCDC) as afunction of the output power of the inverters 13, P_(outINV), for themethod 100.

The curve I_(outDCDCmax) (corresponding to the fixed current I_(F)) isthe current limitation of the DC-DC converter 23 in the third procedure400. It is active when the output power P_(outinv) of the inverter andthe current I_(LS) required by the vehicle loads are high.

The curve P_(outinv)/V_(bat) followed by the second procedure 300represents the condition of equilibrium between input power and outputpower. Above the curve, the DC-DC converter 23 tends to supply morepower than what is regenerated and will hence be periodically disabledin order to balance the average powers. Under the curve, the DC-DCconverter 23 supplies less power than the input power, causing chargingof the storage element C_(DC) and consequent increase in the voltage onthe DC-link bus.

The curve I_(LS) represents the estimate of the vehicle electricalloads. Under the curve the battery is regulated by the alternator. Abovethe curve, the DC-DC converter 23 can contribute to charging of thebattery with the risk of charging it at a voltage higher than the valueset by the energy-management strategy EM (even though the DC-DCconverter 23 is limited in output voltage to a value that is a littlehigher than that of the energy-management strategy EM).

The curves P_(outinv)/V_(bat) and I_(LS) vary, in the directionindicated by the arrows, as the power coming from the inverters 13varies, as the situation of the vehicle loads varies, and moreover asthe value of the battery voltage varies. These quantities are henceconstantly acquired in order to set the optimal value of output currentof the DC-DC converter 23. The dashed curve represents the strategyproposed.

Hence, above the critical power, the shock absorbers 12 generate a powerhigher than the one that it is possible to supply to the vehicleelectrical system in accordance with the settings of energy-managementstrategy EM. These settings are, however, guaranteed by the limitationof current according to the procedure 200 just described.

Also illustrated in FIG. 3A is the detail of the second regulationprocedure 300, which is preferably carried out in the case of brakingand coasting, i.e., deceleration of the vehicle when power is removed,hence in the second mode 120.

In these circumstances, the energy recovered by the energy-recoverymodule 40 is subtracted from the energy that can be recovered from thedeceleration. It is assumed to store electrical energy as much aspossible and then supply it. In the latter step, the behaviour of theDC-DC converter 23 is as in the regulation procedure 200, but at ahigher voltage.

Setting to a high value of battery voltage V_(bat) indicates, in theexample described here, the step of recovery of kinetic energy duringdeceleration or braking. In this situation, the DC-DC converter 23 canbe temporarily disabled, and the energy is stored in the storage elementC_(DC). In this way, it is possible to release, at an instant subsequentto the deceleration step, the energy recovered from the shock absorbers12, preventing it from being subtracted from the kinetic energy. Timing,i.e., the separation in time between the steps of deactivation andactivation of the DC-DC converter 23, depends upon the storage capacityof the storage element C_(DC); hence, the strategy can be convenientlyapplied, for example, in the case of a Li-ion battery. It is envisagedto apply a voltage, for example, of 15.1 V, that is a little higher thanthe value of the reference voltage supplied by the energy-managementstrategy (e.g., 15 V) and to limit the output current to the estimatedload current value I_(LS), as in step 210 of the procedure 200.

Hence, with reference to the flowchart of FIG. 3A, the second regulationprocedure 300 envisages, when a deceleration, in particular due tobraking or coasting, that might be exploited for a procedure of recoveryof kinetic energy is, for example, detected, execution, once again underthe control of the control unit 70, of an operation 310 for disablingoperation of the DC-DC converter 23 by storing in the storage stage 40the energy coming from the energy-recovery stage 30. Then, after a timeinterval T, the length of which depends, for example, upon the storagecapacity of the storage element C_(DC), it is envisaged to carry out anoperation of reactivation 320 of operation of the DC-DC converter 23 bytransferring the energy stored in the storage stage 40.

The length of the time interval depends upon the storage capacity of thestorage element C_(DC) in so far as it is, for example, the timenecessary for the storage element C_(DC) to reach a voltage-thresholdvalue on its own terminals, i.e., on the DC-link bus.

It should be noted that, in the case where the operation of reactivation320 of operation of the DC-DC converter 23 is not sufficient, theadditional loads are activated, as described in what follows.

As mentioned previously, in addition to the first regulation procedure200 there is moreover envisaged a third regulation procedure 400 to beperformed preferably in conditions of acceleration, with rechargingdisabled.

The DC-DC converter 23 can supply power to the battery 14 by regulatingthereon a voltage lower than or equal to the nominal value set by thesmart alternator 60 during the regulation steps on which the procedure200 operates. In this case, particularly valorized is the contributionof the energy-recovery module 30 through the converter 23 in so far asit enables limitation of the energy deficit consequent to disabling ofthe smart alternator 14.

The third regulation procedure 400 envisages—by reading on the LIN a lowvalue of battery-voltage reference V_(bat) ₁₃ _(ref) supplied by theenergy-management strategy EM, for example, 11.8 V, with the aim ofinhibiting charging of the battery by the smart alternator 60, forexample, when occurrence of the condition of acceleration withrecharging disabled is detected—execution by the DC-DC converter 23 ofan operation of setting of its own output voltage at an estimatedbattery-voltage value V_(bats). This estimated value V_(bats) isestimated, for example, on the basis of the recent history of thesettings, for example by calculating a mean value of the last nsettings. It is possible to introduce a safety factor by setting, forexample, a value of 90% of the estimate, to prevent excessive chargingof the battery.

In the steps where, in the third procedure 400, the DC-DC converter 23is disabled, i.e., the voltage on the DC-link bus is below thethreshold, there obtains the regime of energy deficit, with consequentdrop in the battery voltage V_(bat) below the open-circuit voltagevalue.

Alternatively, the DC-DC converter 23 may be configured or controlled toimplement a dedicated charging strategy, which replicates the vehicleenergy-management strategies by thus acquiring the voltage, current,temperature, and battery SOC from the state-of-charge sensor. In otherwords, the DC-DC converter 23 processes its own energy-managementstrategies, substituting them for the vehicle strategies in the casewhere the latter consist in disabling the smart alternator 60 accordingto the procedure 400.

Now that the regulation procedures 200, 300, 400 have been described, acorresponding control loop implemented by the apparatus represented inFIG. 1 is described.

In general, the DC-DC converter 23 must supply current in accordancewith the modalities described previously and at the same time guaranteethe stability of the DC-link bus so that its voltage will be kept withina given range.

Regulation of the output is obtained via an internal current loop (whichis always active) plus an external voltage loop (which is active only incertain operating modes). Limitations of maximum current and voltage arepresent in all of the modes.

FIG. 5 is a more detailed circuit diagram of an example of a converter23 of a buck type.

The DC-DC converter 23 comprises an input capacitance C_(in), connectedbetween the terminal where the input current I_(inDCDC) enters andground. The input capacitance C_(in) can be separated from the storageelement C_(DC) by a filter. Present on said input capacitance C_(in) isthe input voltage drop V_(inDCDC). A switch Q in series separates theinput terminal of the converter 23 from a diode D, set between theswitch Q and ground, with the anode connected to ground. Connected tothe cathode of the diode D is an input terminal of a storage andfiltering inductor L, through which the inductor current I_(L) flows.Connected between the output terminal of the inductor L and ground is anoutput capacitor C_(out), in parallel with the battery 14, whichreceives the current at output from the output terminal I_(outDCDC), andthe output voltage V_(outDCDC) present on the output terminal itself.The output capacitor C_(out) can alternatively be separated from thebattery 14 by a filter.

Shown in FIG. 6 are the currents I_(Q), I_(L), I_(D) in the switch Q, inthe inductor L, and in the diode D during the states of closing (currentI_(Q) higher than zero) and opening of the switch Q. By varying thesestates, regulation in current of the internal loop of the DC-DCconverter is obtained, which hence enables implementation of theregulation procedures 200, 300, 400.

FIG. 7 shows a block diagram of the control loop implemented by theapparatus according to the invention, for the first regulation procedure200. This control loop is implemented in a control module, whichpreferably resides in the DC-DC converter 23.

The battery-voltage reference value V_(bat) _(_) _(ref), set by theenergy-management strategy EM in the control unit 70 according to thefirst, normal, mode (the one that activates the procedure 200),increased by an amount E, is sent to an adder node of the voltage loop,which calculates the error between the battery-voltage reference valueV_(bat) _(_) _(ref) increased by an amount ε and the output voltageV_(DCDC) in the outer regulation loop 24.

This error is supplied to a compensation network with gain G_(comp),which carries out amplification and compensation in order to generate acurrent reference in the inductor I_(LREF) as reference signal for aninternal loop 25, obtained with cycle-by-cycle modulation techniques,which is, for example, hysteretic, of the peak-current-mode type, or ofsome other type, which is aimed at regulating the current I_(L) thatflows in the inductor L, limiting in practice the output currentI_(outDCDC).

This current in the inductor I_(L) results in fact in an output voltageV_(outDCDC) according to a transfer function G_(DCDC) of the converter23, the form of which hence depends upon the topology of converter used.In the case exemplified, this is a topology of a buck type.

Set between the compensation network G_(comp) and the current loop is ablock 27 in which the minimum value is determined according to theoperation 240 and the output current limit value is selected fromP_(in)/V_(bat)+ε′, where the quantity ε′ is a respective currentincrease, I_(LS), and I_(F), this value then being supplied to the innercurrent loop 25.

So far it has been described how the DC-DC converter carries outregulations of its own voltage and current at output, in response todifferent settings of battery-charge voltage defined by theenergy-management strategies.

There is now described a further aspect of the solution disclosedherein, regarding a procedure for regulating the voltage V_(inDCDC) onthe DC-link bus, i.e., the voltage on the storage element C_(DC), whichis set, instead, at the input of the DC-DC converter.

The above voltage V_(inDCDC) is preferably regulated according to ahysteretic mode.

In order to understand the problems of control of the input voltage ofthe converter and on the DC-link bus, already mentioned previously, thestorage element C_(DC) is represented schematically in FIG. 8A andincludes a series resistance R_(ESR) of its own. Appearing alongside, inFIGS. 8B and 8C are, respectively:

-   -   the plot in time t of the current I_(c) in the storage element        C_(DC), which is equal to the difference between the total        current I_(outinv), of the inverter or inverters 13, as in FIG.        1, on the high-voltage bus HV, and the current I_(inDCDC) at        input to the converter 23; and    -   the plot in time t of the voltage drop on the storage element        C_(DC) that includes the series resistance R_(ESR), which        corresponds to the input voltage V_(inDCDC) of the converter 23.

The total current I_(outINV) coming from the inverters 13 has a markedlypulsed nature on account of the damping control strategy. The voltage onthe high-voltage bus HV, or DC-link bus, reflects this behaviour, andmay present of the overvoltages. These overvoltages are of two types:

-   -   peaks PK due to the drop on the series resistance R_(ESR); and    -   progressive rise in the mean voltage (a growing voltage drift DV        represented by a dashed straight line in FIG. 8C) due to the        unbalancing between the output current I_(outinv) coming from        the inverters 13 and current I_(inDCDC) at input to the DC-DC        converter 23.

In order to overcome these problems, represented in FIG. 12 is a circuitdiagram of part of the circuit regarding the side of the high-voltagebus HV. The energy-recovery stage 30 is represented schematically by acurrent generator that sends the output current I_(outINV) of the stage30, i.e., the output current of the inverters 13. A portion I_(C) of theoutput current I_(outINV) flows in the storage element C_(DC), i.e., thecapacitor. The drop on the storage element C_(DC) corresponds to thevoltage V_(DClink) of the high-voltage bus.

There is also envisaged, according to the solution described herein, anadditional load, i.e., a dissipative element, designated by R_(ext), inparallel with the storage element C_(DC). The dissipative elementR_(ext) is connected to ground through a switch B_(ext) controlled by anexternal threshold value, S_(ext), of the bus voltage V_(DClink). Asdescribed more fully in what follows, the external threshold value,S_(ext), is of the type with hysteresis; i.e., it corresponds to anupper threshold S_(ext1) and a lower threshold S_(ext2). Connecteddownstream of the dissipative element R_(ext) is the DC-DC converter 23,which, in the model of FIG. 12, is also connected to the DC-link busthrough a switch B_(DCDC), controlled by a threshold value of the busvoltage V_(DClink) proper to the converter, S_(DCDC). As described morefully in what follows, the converter threshold value S_(DCDC) is of thetype with hysteresis; i.e., it corresponds to an upper thresholdS_(DCDC1) and a lower threshold S_(DCDC2). The switch B_(DCDC) is ineffect here represented as a physical switch, but it is preferably avirtual switch, which is implemented by switching on and switching offthe DC-DC converter 23.

It is emphasised that in general the circuit of FIG. 9 is an alternativeschematic representation of the circuit of FIG. 2, in particularregarding the circuit region of the high-voltage bus and of theconverter 23. The dissipative element R_(ext) in FIG. 2 is notrepresented, but it may equally be present also in the diagram of FIG.2. As illustrated in greater detail in what follows, theenergy-management apparatus implements a method for managing the batterycharge, which envisages control of the voltage on the DC-link asillustrated in what follows, i.e., via a first hysteretic procedure whenthe power P_(outINV), due to the regenerative shock absorber 12, islower than the absorbable power, which is a function of the power thatcan be supplied by the DC-DC converter 23, and via a second hystereticprocedure, which uses the resistance R_(ext) when the power P_(outINV),due to the regenerative shock absorber 12, is higher than the power thatcan be absorbed by the DC-DC converter 23. The output current of theconverter is moreover regulated according to the regulation procedures200, 300, 400 described previously in response to the regulations of thealternator.

The voltage on the storage element C_(DC) is regulated in hystereticmode, as described in what follows.

The output current of the stage 30, I_(outinv), which is a function ofthe damping regulation, tends to cause the bus voltage V_(DClink) torise.

The input current I_(inDCDC), the value of which is a function, throughthe regulation procedures 200, 300, 400, of the energy-managementstrategies, tends to cause the voltage V_(DClink) to drop.

It is hence envisaged to set the external threshold value S_(ext) at avoltage value higher than the threshold value S_(DCDC) of the converter23, for example, at 53 V and 49 V, respectively. In this way, as the busvoltage V_(DClink) increases, first the DC-DC converter 23 is enabledand then, in the case where the voltage continues to rise, the externalload R_(ext) is enabled. Instead, as the bus voltage V_(DClink)decreases, first the external load R_(ext) is disabled and, in the casewhere the voltage continues to drop, the DC-DC converter 23 is disabled.

The switch B_(DCDC) for the DC-DC converter 23, represented in FIG. 12in a purely functional way, may for example be a controlled switch,obtained via a MOSFET, or else, preferably, it may be the control of theconverter 23 that carries out activation/deactivation of the DC-DCconverter 23 itself.

According to the solution described herein, two cases are envisaged.

In the first case, the power P_(outINV), due to the regenerative shockabsorber 12, is lower than the absorbable power by the DC-DC converter23.

In this case, the storage capacitor C_(DC) is hence charged/dischargedby the difference between the power P_(outINV) generated by the inverter13 and the power absorbed by the DC-DC converter 23. The powerP_(outINV) due to the regenerative shock absorber 12 and generated atoutput the inverter 13 is dictated by the workpoint on the dampingcharacteristics of the system of regenerative shock absorbers 12; hence,it cannot be modified or otherwise modulated. The power absorbed by theDC-DC converter 23 can be modulated via cycles of activation anddeactivation of the DC-DC converter 23 according to a hysteretic law,which may be based upon the voltage, in the case where, for example, thestorage element CDC is obtained through chains of supercapacitors (orsupercaps), or else or upon the SOC in the case of a battery 14 ofLi-ion type or of other technology.

The maximum power that can be supplied by the DC-DC converter 23 to thebattery 14 or the low-voltage bus LV is limited by the regulationprocedures 200, 300, or 400 according to the signals of theenergy-management module or by the maximum output current of the DC-DCconverter 23. In either case, if the power P_(outINV) supplied by theenergy-recovery system 30, in particular by the inverter 13, is lowerthan the power that can be absorbed by the DC-DC converter 23, thesystem guarantees total transfer of the recovered energy, varying onlythe working duty-cycle according to the limitation-current value.

The DC-DC converter 23 may hence conveniently be sized in power so as toguarantee the above operating mode with reference to a most likely valueof maximum input power.

In the case, instead, where the power P_(outINV) is higher than thepower that can be absorbed by the DC-DC converter 23, the currentabsorbed by the DC-DC converter 23 is not able to discharge thehigh-voltage bus HV. This may occur on account of the limitation of theoutput current, which is determined by the energy-managementrequirements or else is absolute, i.e., the maximum current that theDC-DC converter 23 is able to supply.

According to a further aspect of the solution described herein, anadditional dissipative load is in this case provided on the high-voltagebus HV itself, as illustrated in FIG. 12. Since, as has been said, thepower coming from the inverters 13 cannot be modified or manipulated,the DC-DC converter 23 is in this case always enabled, with a currentlimitation, whereas the additional load can be modulated according to afurther hysteretic law based upon the voltage of the DC-link (supercaps)or upon the SOC (in the case of a battery of the Li-ion type or of othertechnology).

The level of the voltage, as likewise the corresponding ripple, can bevaried to keep the storage element C_(DC) charged (higher voltage),enabling recovery of the energy previously stored at a moment allowed bythe energy-management strategy EM, or else to keep it discharged (lowervoltage) in order to enable a higher level of storage.

Illustrated, instead, in FIG. 13 are diagrams that represent,respectively, the plots in time t of the output current I_(outINV) ofthe stage 30, of the input current I_(inDCDC) of the converter 23, ofthe current I_(ext) in the external dissipative element R_(ext), and ofthe voltage V_(DClink) on the high-voltage bus.

As may be noted, as long as the output current I_(outINV), supplied bythe inverters 13, remains at a low level, indicating a low recovery, andhence with a power P_(outINV) lower than the power of the converter 23,the voltage V_(DClink) is regulated via cycles of activation anddeactivation of the converter 23, represented by high and low values ofinput current I_(inDCDC) of the DC-DC converter 23. The voltageV_(DClink) remains limited by applying a control procedure of ahysteretic type comprising an operation of threshold comparison withhysteresis of the second voltage value (V_(inDCDC)) with an upperthreshold value S_(DCDC1) and a lower threshold value S_(DCDC2), thevalues of which depend upon the voltage that it is desired to have atoutput from the DC-DC converter 23 according to the operating mode.

When, at a time t_(i), the output current I_(outINV) passes to a higherlevel, representing an output power P_(outINV) generated by the stage 30higher than the power of the converter 23, the current I_(inDCDC)remains fixed at a maximum value, and, whenever the bus voltageV_(DClink) exceeds the external upper threshold S_(ext1), the switchB_(ext) closes, bringing about passage of a current I_(ext) and decreaseof the voltage V_(DClink). When this voltage reaches the external lowerthreshold S_(ext2) of the converter 23, the external switch B_(ext)opens, and the current I_(ext) in the external dissipative elementR_(ext) ceases to flow.

When, at a time t_(f), the output current I_(outINV) returns to a lowlevel indicating an output power P_(outINV) lower than the powerabsorbed by the converter P_(inDCDC), which is at a higher level, thecircuit returns to the first hysteretic control mode, with simpleactivation and deactivation of just the converter 23 in order to remainbelow the threshold S_(DCDC1) established by the energy-managementstrategy EM.

The method for managing the energy supplied to a low-voltage system of amotor vehicle described herein comprises, in the case of an output powerP_(outINV) supplied by the energy-recovery system 30 higher than thepower that can be absorbed by the DC-DC converter 23, providing asdissipative element R_(ext) an additional load circuit 80, connected inparallel between the high-voltage bus HV and ground. This additionalload circuit comprises two tripping circuits for the two types ofovervoltage; namely:

-   -   a first circuit 80H for activation of a high-power load with        fast activation/deactivation, with high triggering threshold        (close to the maximum voltage acceptable on the high-voltage bus        HV, for chopping the peaks), for example, an impulsive power        load; by “fast activation” it is meant that the first activation        circuit 80H must have a time constant sufficient to follow the        peaks PK of the high voltage, i.e., comparable with the time        constant associated to the peaks PK of the high voltage; in        particular, the activation must be fast and hence must be based        upon an instantaneous reading of the voltage, such as the one        that can be obtained via a peak detector; and    -   a second circuit 80L for activation of a low-power load with        slow activation/deactivation, with a threshold around the        nominal voltage of the high-voltage bus HV and possibly        variable, with the aim of keeping the mean voltage of the        high-voltage bus HV at the desired value even in the presence of        power unbalancing (I_(outINV)>I_(in) _(_) _(DCDC)); for        instance, it may be a medium-power load with slow activation; by        “slow activation” it is meant that the second activation circuit        80L has a time constant such as to follow the increase of the        mean value, i.e., the voltage drift DV indicated in FIG. 8C,        i.e., a time constant comparable to the time constant associated        to the increase of the mean value; for this type of regulation,        a filtered reading of the voltage becomes necessary.

It should be noted that, in variant embodiments, the additional loadcircuit may comprise only the first activation circuit 80H or the secondactivation circuit 80L.

As illustrated in FIG. 12, the circuit 80 comprises a fast-activationbranch 80H, which includes a peak detector 82 and a circuit 84H forcontrol of the gate of a MOS 81H, the drain of which is connected, via afast-circuit resistor R_(H) _(_) _(ext), to the high-voltage bus HV,whereas the source electrode is at ground. When the gate-control circuit84H, on the basis of the value detected by the peak detector 82, detectsthat the input voltage V_(inDCDC) of the converter 23 is above a giventhreshold, for example, the external upper threshold S_(ext1), itactivates the gate of the MOS 81H to close the MOS 81H, whichsubstantially operates as switch so that the fast-circuit resistor R_(H)_(_) _(ext) connected between the high-voltage bus HV and groundoperates as dissipative load for the excess power.

Moreover, the circuit 80 comprises a slow-activation branch 80L, whichincludes a filter 83 and a circuit 84L for control of the gate of a MOS81L, the drain of which is connected via a slow-circuit resistor R_(L)_(_) _(ext), to the high-voltage bus HV, whereas the source electrode isat ground. The filter 83 carries out filtered reading of the inputvoltage V_(inDCDC) of the converter 23.

When the gate-control circuit 84L, on the basis of the value filtered bythe filter 83, detects that the input voltage V_(inDCDC) of theconverter 23 is above a given threshold, for example, the external lowerthreshold S_(ext2) that is a little higher than the nominal voltage andmuch lower than the threshold of the circuit 80H, it activates the gateof the MOS 81L to close the MOS 81L, which substantially operates asswitch so that the resistor R_(L) _(_) _(ext) connected between thehigh-voltage bus HV and ground operates as dissipative load for theexcess power.

FIG. 12 illustrates a circuit detail of the additional circuit 80, whichshows the peak detector 82 of the high-voltage circuit 80H, comprising adiode Dp, the anode of which is connected to the high-voltage bus HV andthe cathode of which is connected to the input of the gate-controlmodule 84H, i.e., to the input of a comparator 831, to evaluate whetherthe voltage on the anode of the diode Dp is higher than a giventhreshold. Connected to the input of the comparator 831 are acapacitance Cp towards ground and a resistance Rp in parallel thereto.The comparator 831 is connected to a gate driver 832, which supplies thecurrent for driving the gate electrode of the MOS 81H.

The slow-activation circuit 80L is similar to the fast-activationcircuit 80H, but comprises an RC filter, including a resistor R_(f),which is connected to the high-voltage bus HV and is set in series witha filter capacitor C_(f), which is in turn connected to ground.Connected between the resistor R_(f) and the capacitor C_(f), where avoltage filtered with respect to the input voltage V_(inDCDC) is set up,is the input of the gate-control module 84L.

The aim is to dissipate the excess power on loads external to the DC-DCconverter 23 so as to minimise thermal sizing thereof, whence thepreference for a PWM (Pulse Width Modulation) control for the additionalloads.

In addition to the solution of FIG. 12, also possible is a mixed controlsolution, for example, with MOSFETs that drive the external loads inlinear mode, in particular for the circuit 80H. In this regard,illustrated in FIG. 13 is a variant in which, instead of the peakdetector 82 and the gate control module 84H, a circuit 82′ is provided,which comprises a diode D1, connected with its anode to the high-voltagebus HV and with its cathode to the cathode of a Zener diode Dz. Theanode of the Zener diode Dz is connected, through a resistor R_(z), toground and to the gate of the MOS 81H. When the input voltage exceedsthe breakdown voltage of the Zener diode Dz, the MOS 81H enters intoconduction, activating the fast-activation load R_(H) _(_) _(ext).

To contain the size of the additional load 80 it is possible to activatevehicle loads that are typically slow, for example, the heated rearwindow after previously checking that the consequent raised currentlimitation for the current loads is lower than the absolute one:otherwise, energy (supplied by the alternator) is wasted.

Hence, from the foregoing description, the advantages of the presentsolution emerge clearly.

Advantageously, the apparatus and method described enable control of thevehicle low-voltage bus in the presence of a number of power-generatingdevices, such as the alternator and regenerative shock absorbers, inaccordance with the existing energy-management strategies, in particularwith the voltage set by the smart alternator.

Furthermore, the apparatus and method described enable operation of theDC-DC converter so as to regulate the output current (and voltage) andthe input voltage simultaneously.

In addition, the apparatus and method described enable operation in thecases where the battery-voltage set point is not available, as in thecase of the classic alternator or of a smart alternator duringacceleration.

Moreover, the apparatus and method described additionally enablehandling of the cases where the power supplied by the energy-recoverystage is higher than the absorbable power at output from the DC-DCconverter.

Of course, without prejudice to the principle of the invention, thedetails of construction and the embodiments may vary widely with respectto what has been described and illustrated herein purely by way ofexample, without thereby departing from the scope of the presentinvention.

For instance, the energy-recovery system, instead of or together withthe regenerative shock absorbers may comprise regenerative brakes.

What is claimed is:
 1. An apparatus for managing the energy supplied toa low-voltage system of a vehicle that comprises an energy-recoverystage, said low-voltage system, which operates at a first voltage,comprising: a battery, which supplies said first voltage on alow-voltage bus; a system for charging the battery, which comprises analternator for supplying a charging voltage to said battery; and vehicleloads, which are supplied by the battery and/or by the alternator, saidvehicle comprising a high-voltage system, operating at a second voltagehigher than said first voltage, said system comprising said vehicleenergy-recovery stage, which supplies said second voltage, said secondvoltage being supplied through an intermediate energy-storage system toa DC-DC converter, which converts said second voltage into said firstvoltage on said low-voltage bus, including a module for regulating thealternator having at least one first operating mode in which thealternator regulates a voltage of the battery at a nominal operatingvalue, wherein said apparatus detects information on the regulatedvoltage in order to detect the operating mode of the alternator; andupon detection of said first operating mode, said apparatus carries outa procedure for regulation of the DC-DC converter, which comprises: anoperation, in which a current required by the vehicle loads isestimated; an operation, in which the value of current determined by theratio between the power supplied by the energy-recovery stage and thebattery voltage is calculated; an operation, in which a pre-set fixedcurrent value that enables sizing of the DC-DC converter at a givenvalue of desired average transferrable power is considered; an operationof evaluating the lowest of said three values, namely, the estimatedrequired current, the current value determined by the ratio, and thepre-set fixed current value; and an operation of limitation, via theDC-DC converter, of the output current to the lowest of said threevalues, namely, the estimated required current, the current valuedetermined by the ratio, and the pre-set fixed current value.
 2. Theapparatus as set forth in claim 1, wherein it comprises a control modulethat performs energy-management operations at least by the alternator,which supplies, as information on the regulated voltage, abattery-voltage reference.
 3. The apparatus as set forth in claim 1,wherein said control module manages the energy of the alternator,comprising a second operating mode in which the alternator regulates thevoltage of the battery at a battery-voltage value increased with respectto the second nominal voltage, and, if said second operating mode isdetected, the apparatus performs a procedure of regulation of the DC-DCconverter, which comprises: an operation for disabling operation of theDC-DC converter by storing in the intermediate energy-storage system theenergy coming from the energy-recovery stage; and after a given timeinterval, in particular a time interval necessary for a storage elementof the intermediate energy-storage system to reach a voltage-thresholdvalue on its terminals, reactivation of reactivating the operation ofthe DC-DC converter by transferring the energy stored in theintermediate energy-storage system.
 4. The apparatus as set forth inclaim 1, wherein said control module manages the energy of thealternator, comprising a third operating mode in which the alternatoroperates so as to regulate the battery voltage at a value lower than thefirst nominal voltage, and the apparatus regulates the DC-DC converter,including supplying power to the battery by regulating a voltage lowerthan or equal to the value of the first nominal voltage, in particularby carrying out an operation of setting a battery-voltage valueestimated on the basis of the recent history of the settings.
 5. Theapparatus as set forth in claim 1, wherein said operation of detectionof said first, second, or third operating mode comprises detection of abattery-voltage reference controlled by said control or regulationmodule for carrying out energy-management operations.
 6. The apparatusas set forth in claim 1, wherein said vehicle energy-recovery stage thatsupplies said second voltage comprises one or more regenerative shockabsorbers and/or one or more regenerative brakes.
 7. The apparatus asset forth in claim 1, wherein: the second voltage of said DC-DCconverter is regulated via a control procedure of a hysteretic type,which comprises an operation of threshold comparison with hysteresis ofthe value of the second voltage and activates or deactivates said DC-DCconverter on the basis of the result of said comparison operation; saidenergy-management apparatus comprises an additional load set in parallelto the input of the converter, which can be selectively connected to thehigh-voltage bus; and if the power supplied by the energy-recovery stageis higher than a power absorbed by the converter, the apparatus keepsthe DC-DC converter always activated, with a current limitation, inparticular according to said first, second, or third operating mode, andfor selecting the connection of the additional load according to afurther hysteretic control procedure, in particular based upon thesecond voltage or upon the state of charge.
 8. The apparatus as setforth in claim 7, wherein said further hysteretic control procedurecomprises respective thresholds for the additional load and for theconverter and envisages setting the threshold value that controlsselective connection of the additional load to the high-voltage bus at avoltage value higher than the threshold value of activation of theconverter, so that, as the second voltage increases, first the DC-DCconverter is activated and then, in the case where the voltage continuesto rise, the additional load is activated, and, instead, as the secondvoltage decreases, first the additional load (R_(ext)) is deactivated,and then, in the case where the second voltage continues to drop, theDC-DC converter is deactivated.
 9. The apparatus as set forth in claim1, wherein it comprises an additional load circuit connected in parallelbetween the high-voltage bus and ground, which comprises a first circuitfor activation of a faster-activation load, with higher triggeringthreshold, and/or a second circuit for activation of a slower-activationload, with threshold higher than the second nominal voltage of thehigh-voltage bus and lower than said higher triggering threshold. 10.The apparatus as set forth in claim 1, wherein said apparatus detectsinformation on the regulated voltage in order to detect the operatingmode of the alternator by estimating the value of a charging voltage(V_(ALT)) of the battery on the basis of detection of its value in oneor more working steps of the apparatus in which there is no transfer ofenergy from the DC-DC converter.
 11. A method for managing the energysupplied to a low-voltage system of a vehicle, said vehicle comprising alow-voltage system and a high-voltage system as set forth in claim 1,comprising activating at least one first operating mode, in which thealternator regulates a voltage of the battery at a nominal operatingvalue; wherein said method includes the steps of: detecting informationon the regulated voltage in order to detect said operating mode of thealternator; upon detection of said first operating mode, carrying out aprocedure of regulation of the DC-DC converter, comprising: anoperation, in which a current required by the vehicle loads isestimated; an operation (in which the value of current determined by theratio between the power supplied by the energy-recovery stage and thebattery voltage is calculated; an operation in which a pre-set fixedcurrent value that enables sizing of the DC-DC converter at a givenvalue of desired average transferrable power is considered; an operationof evaluating the lowest of said three values, namely, the estimatedrequired current, the current value determined by the ratio, and thepre-set fixed current value; and an operation of limitation, by theDC-DC converter, of the output current to the lowest of said threevalues, namely, the estimated required current, the current valuedetermined by the ratio, and the pre-set fixed current value.
 12. Themethod as set forth in claim 11, further comprising the steps ofcarrying out energy management by the alternator, including a secondoperating mode in which the alternator regulates the voltage of thebattery at a battery-voltage value increased with respect to the secondnominal voltage, and, if said second operating mode is detected, theapparatus carries out a procedure of regulation of the DC-DC converter,which comprises: an operation for disabling operation of the DC-DCconverter by storing in the intermediate energy-storage system theenergy coming from the energy-recovery stage; and after a given timeinterval, in particular a time interval necessary for a storage elementof the intermediate energy-storage system to reach a voltage-thresholdvalue on its terminals, carrying out an operation of reactivation ofoperation of the DC-DC converter by transferring the energy stored inthe intermediate energy-storage system.
 13. The method as set forth inclaim 11, wherein it comprises carrying out energy management by thealternator, comprising a third operating mode in which the alternatorregulates the battery voltage at a value lower than the second nominalvoltage, and the apparatus carries out a procedure of regulation of theDC-DC converter, which comprises supplying power to the battery byregulating a voltage lower than or equal to the first nominal voltagevalue, in particular by carrying out an operation of setting abattery-voltage value estimated on the basis of the recent history ofthe settings.